In recent years, the public has become increasingly aware of the deteriorating quality of our nation's and the world's water supply. Pollutants, biological and toxic waste and other contaminants are being introduced into water supplies at an ever increasing rate, making such water supplies unfit for drinking and other necessary uses. For example, medical patients with low immunity are now being requested not to drink tap water, and disease and illnesses linked to poor quality drinking water have increased dramatically in recent years. This problem is especially significant outside the United States where water quality has deteriorated to an all time low, with the major source of such contamination primarily being bacterial in nature. Many known solutions that currently exist to purify water, however, generally are too expensive or are not feasible in certain locations.
Of current filtration systems available, reverse osmosis systems are one of the most common solutions for improving water quality. Generally, these systems use a sediment removal filter in conjunction with activated carbon and a bacteriostatic membrane coated with oxides and halide of silver, as described in detail by Nishino in U.S. Pat. No. 3,872,013, placed between the filter and the water outlet. The membrane will prevent certain bacteria from leaving the filter and will retard their growth on the surface of the membrane, but will not check bacterial growth on the activated carbon or the ability of bacteria to multiply and produce toxins. Other mechanical filters such as ceramic filter cartridges that filter out bacteria of about 1 micron in size also are ineffective in retarding bacterial growth as the bacteria are collected on the surface of the filter.
Another type of biocidal reverse osmosis system is described in detail by Von Medlin in U.S. Pat. No. 5,269,919. Von Medlin further teaches the use of a polyiodide resin that releases iodide upon contact with bacteria and viral organisms to combat bacterial growth, and uses granular metal alloys and activated carbon to remove iodides released in the water. If not removed, these iodides would be harmful to human beings. In fact, EPA "Policy on Iodine Disinfection", initially developed in 1973 and reaffirmed in 1982, is that iodine disinfection is for short-term only, whenever iodine-containing species remain in the drinking water.
Thus, it appears that while a portion of the bacteria within the water supply will be caught by these filters, such trapped bacteria are allowed to grow within present water purification systems. Thus, the filters become a breeding ground for bacteria and toxins, possibly subjecting persons to potential harm by ingestion of toxic trace metals such as silver and copper halides, and other contaminants not filtered out of the water.
There has also been considerable development in wound or wrapped filters in which yarns are wrapped in varying patterns and layers about a perforated core. Increasing the number of layers and the tightness of the wrapping of the yarns generally has been found to be more effective at trapping particulate matter in the filter, but also suffers from the drawback of restricting the flow of water through the filter, thereby causing a pressure drop in water flow through the system. Typically, water pressure in a municipal water line in the United States runs between 60-80 psi. As conventional wound filters become more particulate laden, the pressure drop in the line caused by the restriction in water flow through the water filter increases upwards of 15-20 psi or greater. Such a pressure drop is an even greater problem overseas as line pressures generally are lower, on the order of 35 psi or less, so that the use of such filters cause the water flow to be so significantly restricted as to unduly limit the system.
In addition, activated carbon currently is used in many types of filters for removing odors, dissolved organics and unpleasant tastes from water supplies. A drawback to using activated carbon in filters is, however, that carbon is a source of nutrients for bacteria and once infected, carbon filters generally allow rapid multiplication of bacteria on the filters. As a result, carbon filters generally are required to have a warning to use only microbiological safe water for filtration through such filters. As a consequence, in many countries outside the U.S., where waters are not safe from microbiological contaminants, the use of such carbon filters can be dangerous and thus is generally not feasible. This has led to regulations banning the use of carbon in filters for certain uses and in certain areas.
It therefore can be seen that a need exists for an inexpensive and safe to use filter cartridge for a water filtration system that can filter microscopic organisms and prevent bacterial and viral growth within the filter media, without releasing life harming biocides that have to be further filtered out and which does not unduly restrict water flow through the system.